The present invention relates to an electrical connector and, more particularly, to an electrical connector assembly especially useful for detachably engaging electrically with a high-density arrangement of interchangeable conductors and for systematically routing the resulting current to an even higher-density arrangement of indexed conductors.
Such an electrical connector assembly finds particular application in the area of computer mainframe connections where, for example, the indexed conductors represent a row(s) of conductive traces on a circuit board of a mainframe computer and where the interchangeable conductors represent coaxial or twisted wire cables leading to respective control panels, monitors, printing devices, or other input/output devices. In this type of exemplary environment, the critical features of an electrical connector array include its serviceability, its high frequency capability, its systematic routing capability, and its densifying capability. These features, in view of existing devices, will now be examined in turn.
At the detachably engaging end of the connector assembly is a contact array including discrete contacts typically requiring periodic serviceability. Such contacts may be forks, for example, each having a pair of tines that mechanically engages a respective pin-like terminal, as shown, for example, in Cacolici U.S. Pat. No. 4,094,564, Webster U.S. Pat. No. 4,310,208, and Sitzler U.S. Pat. No. 4,327,956. Such pin-like terminals may extend from a terminator block into which individual interchangeable conductors have been terminated. Such terminator blocks can be designed for separate insertion in, or removal from, the back of an insulative block contained inside the frame of a mating connector assembly as shown, for example, in Tengler et al., U.S. Pat. No. 4,484,792.
Occasionally, a connect/disconnect operation between a particular fork-like contact and a pin-like terminal of a particular terminator block will break or bend the fork or cause insulative material to be scraped from the separate insulative block surrounding all of the forks. This impairs the quality of the resulting electrical connection and makes connector serviceability down to the contact level highly desirable.
Ever increasing computer processing speeds have made the high frequency properties of the connector assembly critical. At increasing frequencies the conductors of the assembly function as antennaes and therefore they must be isolated from externally generated signals as well as from adjacent signal lines that would otherwise cause cross-talk. In addition, the electrical lengths associated with different contacts in the assembly cannot be so diverse as to cause significant delays among the high-frequency signals carried by the contact array.
The systematic routing capability of the electrical connector assembly is important because of the high number of signal lines associated with a mainframe computer. If a particular contact, in a particular position at the engaging end of the contact array, is always associated with a specific signal trace on a board inside the computer, then this prevents misconnection of external equipment. For example, there may be three discrete contacts that are unengaged but the user will be able to tell, by the respective positions of the unengaged contacts, which contact he should mate his desired interchangeable conductor with. Of course the user could test the computer output at each engaging contact to determine which contact he wants, but this requires much more time.
The densifying capability of the electrical connector array is especially important so that current may be routed from a high-density environment of the interchangeable conductors to an even higher-density environment of the indexed signal traces on the computer board. Although large scale integration (LSI) has vastly increased the computing power-to-size ratio of computer mainframes, the dimensioning capability of present day electrical connectors has not kept pace with this scale reduction in circuit technology, and the improved power-to-size ratio, to some extent, has been wasted.
Although attempts have been made to improve the densifying capability of electrical connectors, each attempt has lead to a commensurate, and unacceptable, reduction in serviceability, high frequency performance or systematic routing capability of the electrical connector. The first difficulty arises at the detachably engaging end of the contacts where the width of the mechanical tines on each discrete contact, although necessary to make each contact detachably engageable, sets a limit on how closely the contacts may be spaced together. When the widths of each tine are summed together the resulting sum is the maximum contact "footprint" measurable, for example, if the contacts were placed on a level surface, side-by-side, touching each other. Generally, from each discrete contact extends a terminal, such terminal including a neck portion and a lead portion, whereupon the lead portions of all of the terminals together form a coplanar layer. The primary difficulty arises in minimizing the spacing between respective leads and minimizing total contact footprint without degrading high frequency performance. For example, the required lead spacing may be achieved solely by the use of bends in the terminal necks, but this does nothing to reduce the maximum contact footprint. Such an approach also results in each adjacent contact/neck/lead assembly having its own unique physical shape and electrical length, thereby greatly increasing manufacturer tooling costs and degrading high frequency performance. By vertically overlapping adjacent contacts one may reduce the total contact footprint, and decrease the lead spacing as well, but each assembly still has a unique physical shape and electrical length. Furthermore, at high frequencies, the wide conductive surfaces of the contacts will tend to capacitively couple thereby inducing cross-talk between adjacent signal conducting contacts. A conventional approach, that does improve densifying capability, while also addressing high tooling cost and degraded high frequency performance, is a division of the contacts into a top and bottom group, where a straight neck portion extending upwardly from a bottom contact is followed by a straight neck portion, of equal length, extending downwardly from a top contact and vice versa. Each contact/neck/lead assembly may then have the same physical shape and electrical length, greatly decreasing tooling costs and improving high frequency performance, Additionally, capacitive coupling will be improved over the vertically overlapping aproach because, given a lead spacing equalling half the connector width, for example, the flat surfaces of the contacts will be arranged in side-by-side, rather than in overlapping, relationship. With this approach, however, the contact footprint will approach, but never be less than, half the maximum contact footprint. Additionally, if the necks are bent to further reduce lead spacing (otherwise the use of straight necks sets the minimum lead spacing at one-half the width of each contact) then the contact/neck/lead combinations will no longer have equal physical shape thereby reestablishing increased tooling costs.
In addition to the limiting factors just discussed, the minimum lead spacing obtainable will be determined by the size of the leads themselves and by cross-talk requirements. If the widths of the leads are reduced, without reducing the spacing between each respective lead, this reduces cross-talk between adjacent signal conducting leads but makes each individual lead susceptible to breakage or to being bent out of position (thus destroying systematic routing capability or creating signal shorts). Although the dimensional gap, between the narrow semirigid leads and the even narrower indexed conductors, may be made using thin insulative wires (that are less susceptible to breakage because of the cushioning effect of the insulation) such discrete wires are easily mispositioned (non-systematically routed) therefore creating excessive assembly errors. Another possible means of bridging the dimensional gap is to use ribbon cable. This eliminates systematic routing problems because of the ordered arrangement of the ribbon conductors. However, the ribbon conductors may only be made so thin before problems are encountered, such as breakage of the conductors when the ribbon cable is stripped or such as breakage of the conductors when the ribbon conductor-to-lead connection is moved slightly due to connector insertion forces.